inside-root.swift

// https://twitter.com/koher/status/1627284858493075463
for n in 2 ... 1000000 {
    var a = n * n - 1
    while a.isMultiple(of: 2) {
        a /= 2
    }
    while a.isMultiple(of: 5) {
        a /= 5
    }
    guard a == 1 else { continue }

    var b = n * 10
    while !b.isMultiple(of: n * n - 1) {
        b *= 10
    }
    print(n, b / (n * n - 1))
}